SK19132000A3 - Catalyst for steam cracking reactions - Google Patents

Abstract

Catalyst for steam cracking reactions consisting of crystalline calcium aluminates having a molar ratio CaO/Al2O3 ranging from 1/6 to 3 and of molybdenum and/or vanadium oxides, wherein the molybdenum oxide, expressed as MoO3, or the vanadium oxide, expressed as V2O5, or the sum of said two oxides, is in a quantity ranging from 0.5 to 10%, preferably from 0.8 to 5% by weight. <IMAGE>

Description

Technical field

The present invention relates to a catalyst for steam cracking reactions.

BACKGROUND OF THE INVENTION

Light olefins, especially ethylene and propylene, are among the most important chemical products of the petrochemical industry. Ethylene is more than 75 million euro in terms of production volume. tons per year fourth in the world and propylene is 13th in a row. The industrial importance of ethylene is also evident from the range of products made from this material. About 80% of the total ethylene production is for the synthesis of thermoplastic polymers. Ethylene alone is a monomer for the production of polyethylene and is a raw material for other important monomers such as vinyl chloride, vinyl acetate and ethylene glycol. Some of these compounds also have non-polymeric uses, for example ethylene glycol is a major component of antifreeze. Given the industrial importance of ethylene and propylene, which need to be produced in large volumes, it can be assumed that improving production processes that even in some way would increase the yield of light olefins could bring significant economic benefits.

The main source of ethylene and propylene is steam cracking, which is a thermal process derived from

e. a cracking process in which the hydrocarbon feedstock is heated in the presence of water vapor in special furnaces to produce an olefin rich gas stream. For many years, attempts have been made to improve this manufacturing process, which focuses on furnace technology, while attempts have been made to improve heat exchange, reduce residual time, and optimize the geometry of pyrolytic tubes.

Limited research was also conducted in a less conventional direction and focused on a catalyst that would be effective in steam cracking reactions and improve light olefin yields.

However, it has to be noted that the use of a catalyst for steam cracking reactions has not been studied to a wider extent, although research has been undertaken by various companies and research teams since the 1970s. In some cases, the process itself has been defined, but so far no industrial applications have been published and are not known.

In many cases, the test catalyst comprises a zeolite component.

One of the main examples is associated with Asahi Chemical, which has filed various patents on this subject, see for example JP-06/346062 (20/12/94); JP-06/199707 (19/07/94); JP-06/346063 (12/20/94); WO-96/1331 (09/05/96).

Asahi claims a circulating bed steam cracking process that uses a ZSM-5 and ZSM11 zeolite catalyst on which metals such as iron, magnesium and / or metals Ib are absorbed. groups, preferably silver. This way

r. r J ttw e · e e c ♦ r y r y r y r y, r y r y r-y r CCC y y r?

r c c r. . · Λ

Crrrrrr -rrrrr0 partially increases ethylene yield, but the reaction focuses mainly on the production of propylene and aromatic hydrocarbons. Recent information (for example, "Ethylene Via Catalytic Naphtha Cracking" PERP Report 96 / 97S 12-Chem. Systems, September 1997) revealed that this method still presents serious technological problems that still need to be addressed before commercialization of the process, these problems relate to the catalyst (regeneration efficiency, durability).

SINOPEC (China) proposes a catalyst containing zeolite, in particular zeolite Y and zeolites with a pentasyl structure, high in silicon, containing P-Al or P-Mg or P-Ca (EP-909582). Another zeolite-based catalyst system was developed by the University of Ghent in cooperation with Amoco. These are zeolite-based catalysts HZSM-5 containing P-Ga, which increase propylene yield in oil cracking (W. De Hertog, GF Froment, MP Kaminsky, Proc. AICHE 1999 Spring National Meeting, 14-18 March 1999, Houston , USA); however, even in this case, the effect of the catalyst on ethylene due to its acidic character is minimal.

Another type of catalysts studied in the steam cracking reactions are aluminum-calcium compounds. These solid materials, unlike zeolites, increase the yield of light olefins without significantly altering the quantitative ratios between the major products. In this way, an increase in propylene yield as well as ethylene yield is achieved. Various mixtures have been proposed in which some compounds always predominate, for example, by CaO.Al ₂ O ₃ and CaO ₂ Al ₂ O ₃ proposed by Nowak et al. (DD-243 647 of 1987) or the Mayenite phase (12 CaO 7 Al ₂ O ₃ ) reported as the predominant compound by rrrrerr; frr · frr r-eef 'rr''cirnr designed by Lemonida and Vasalos (AA Lemonida, IA Vasalos, Applied. Catalysis, 54, 1989, and AA Lemonida, IA Vasalos, t EJ Hirschberg, RJ Batalacini, Idustrial Engineering Chemistry Res., 28 , 1989) University of Thessalonica in cooperation with Anoce.

I

In a previous work, mayenite has been identified as the most effective crystalline phase among calcium aluminates in steam cracking reactions and therefore the work focused on obtaining this compound in pure form (first patent - H9040). Some authors have added metals to aluminum catalysts to improve the performance of catalytic systems. Various experiments carried out with alkali metals (especially potassium), the primary aim of which is to reduce coke production, can be read from the literature. The presence of alkali metals does not, in fact, contribute to the reduction of coke production, but causes a significant increase in other undesirable by-products, such as carbon monoxide, whose yields vary in percentages. In addition, significant amounts of potassium were lost in the tests (see R. Mukhopadhyay, D. Kunzru, Industrial Engineering Chemistry Res., 32, 1993).

It has been found that the efficiency of aluminum-calcium compounds in steam cracking reactions can be increased by the addition of transition metals such as molybdenum and vanadium. In fact, these elements, when added to the base catalyst in the form of oxides, will allow a further increase in the yield of the major desired products, ethylene and propylene. The negative impact on by-product formation, such as coke and carbon monoxide, is limited, and in fact these by-products in tests conducted with primary gasoline did not exceed 1% by weight. yield, related r r, c r. r e r C r, r r r <<r r r r (r r to the weight of the starting material, even in the presence of a molybdenum or vanadium modified catalyst)

SUMMARY OF THE INVENTION

The catalyst for steam cracking reactions according to the invention consists of crystalline calcium aluminates having a CaO / Al ₂ O ₃ molar ratio of 1/6 to 3 and molybdenum and / or vanadium oxides, the molybdenum oxide expressed as MoO ₃ or the vanadium oxide expressed as V ₂ O ₅ or the sum of the two oxides is contained in the catalyst in an amount ranging from 0.5 wt. % to 10 wt.%, preferably from 0.8 wt. % to 5 wt.

The process for preparing this catalyst is characterized in that it comprises the following steps:

dissolving the molybdenum or vanadium-containing salt in a suitable solvent;

impregnating the calcium aluminate present in the form of granules by adding said aluminate to the molybdenum or vanadium salt solution;

elimination of the solvent;

drying the solid precursor product at temperature

100 ° C to 150 ° C;

- annealing the solid precursor product at temperature

500 ° C to 650 ° C for at least 4 hours.

yy yy yy yy yy yy yy yy yy yy yy yy yy yy yy yy yy yy yy

- r r - r r - c - c

The choice of solvent depends on the salt selected and is preferably selected from water, alcohol, ether, acetone, the most preferred solvent for dissolving the molybdenum salt is water and for dissolving the vanadium salt is ethanol.

. ¹ . 1

The crystalline calcium aluminates forming the catalyst should be selected from aluminates having a CaO / Al ₂ O ₃ molar ratio ranging from 1/6 to 3, and more preferably reaching 12/7 or 3.

The same applicant in a non Italian patent application claimed a pure mayenite having the general formula 12CA / 7AL ₂ O 3 having, in its calcined form of an X-ray diffraction spectrum recorded with a vertical goniometer fitted with a pulse electron beam by reading a CuKa radiation (λ = 1.54178 × 10 ¹⁰ m) containing the main reflections outlined in Table I (where d denotes the interplanar distance); and FIG. First

This pure mayenite may advantageously be selected as the calcium aluminate used to prepare the catalyst of the invention.

The process for preparing pure mayenite described above comprises the following steps:

- dissolving calcium and aluminum containing salts in water;

complexing the dissolved salts with polyfunctional organic hydroxy acids;

drying the solution obtained in the preceding step to form a solid precursor product;

r e e r ** r c - * c

c. e e ♦ e r r · r e · e e r r> r cr e r r y r. - · · o r n f · o r n f. . r r o r n c o c <i. ' c ·. · · r · n o

- annealing the solid precursor product at a temperature of 1300 ° C to 1400 ° C, preferably 1330 ° C to 1370 ° C, for at least 2 hours and preferably at least 5 hours.

The polyfunctional organic hydroxy acids may be selected from citric acid, maleic acid, tartaric acid, glycolic acid and lactic acid, with a preferred polyfunctional organic acid being citric acid.

The calcium-containing salts are preferably selected from calcium acetate and calcium nitrate.

Aluminum nitrate is the preferred aluminum-containing salt.

This process is recommended to be carried out at a molar ratio of polyfunctional hydroxyacids / salts containing calcium and aluminum of 1.5 to 1.

A further object of the invention relates to a process for the production of light olefins by steam cracking of a hydrocarbon feedstock selected from petroleum, and in particular a primary gasoline, kerosene, gas oil or mixtures thereof in the presence of a catalyst according to the invention, which is preferably effective at 720 ° C to 800 ° C and a pressure of 111 kPa to 182 kPa during a contact time of 0.07 to 0.2 s.

Exemplary embodiments of the invention will now be described, which are illustrative only and do not limit the scope of the invention, which is clearly defined by the appended claims.

DETAILED DESCRIPTION OF THE INVENTION

Example 1

Preparation of pure mayenite

I ·

The synthetic method used in a homogeneous phase was used.

The method involves the use of citric acid or polyfunctional hydroxy acids which make it possible to form metal salt complexes in aqueous solution. After dehydration of the aqueous solution, an amorphous solid precursor is obtained which, after heat treatment at high temperature, yields the desired product. The main advantages of this technique are:

homogeneous mixing over the range of atoms;

- good stoichiometry control;

- production of mixed oxides using commercial chemical products;

- short operating times.

A solution of aluminum nitrate, 378.2 g Al (NO ₃ ) ₃ .9H ₂ O (1.008 mol) in 470 g water, was first added to a solution of calcium acetate, which was prepared by dissolving 152.2 g (CH ₃ COO) 2 Ca. H 2 O (0.864 mol) in 450 g H ₂ O at room temperature. A solution of citric acid, 393.1 g (1.872 mol) in 375 g of water was then added. The obtained homogeneous solution was dried using a spray dryer. The desired product 12CaO.7Al R ₂ O ₃ · y '(Mayenite) was obtained after 5 hours of annealing at 1350 ° C in pure form.

Prior to tabletting the catalyst precursor, a lubricant (2 wt% stearic acid) was added to the precursor and after tableting the catalyst was further annealed.

The composition of the obtained catalyst was verified by X-ray diffractometry, which showed the presence of a single pure mayenite phase.

(See Table I and Fig. 1 above)

Example 2

Preparation of mayenite (12CaO.7Al ₂ O ₃ ) enriched with 2% MOO3

In a 250 cm ³ flask was placed 0.86 g of ammonium heptamolybdate (0.0049 mol) in 100 g of water. 35 g of granulated mayenite (20 to 40 mesh) was added to the solution. After 2 hours, the product was dried and subsequently calcined at 550 ° C for 5 hours.

The composition of the obtained catalyst was verified by X-ray diffractometry (Table II and Fig. 2), from which it can be seen that further processing of molybdenum did not alter the crystalline structure of mayenite.

A small amount of CaO may be formed which does not affect the activity of the catalyst.

^r c

Example 3

Preparation of Mayenite enriched with 2% V2O3

In a 250 cm ³ flask was placed 2.68 g of vanadium acetylacetonate (0.0077 mol) in 75 g of ethanol. 35 g of granulated mayenite (20 to 40 mesh) was added to the solution. After 2 hours, the product was dried, followed by calcination at 550 ° C for 5 hours.

Example 4

Steam cracking reaction carried out in a laboratory pulse operation

Operating conditions:

charge = primary gasoline temperature = 775 ° C

H ₂ O / charge = 0.98 wt.

dwell time -0.15 s time in current = 60 s

Table III contains the data obtained using an aluminum-calcium catalyst prepared as described in Example 1, the use in steam cracking of naphtha and compared with the results of a test using the same molybdenum oxide-enriched catalyst prepared by is described in the example

2. It is apparent from these data that the performance of the non-enriched catalyst does not achieve the results obtained when using a molybdenum-containing catalyst in terms of ole light olefin yield.

r rt r r

The increase in the yield of ethylene and propylene in the case of the enriched catalyst is 5.3%, as opposed to the non-enriched catalyst.

Example 5

I

Steam cracking reaction carried out in a continuous laboratory equipment equipped with a 1,25 cm fixed bed reactor

Operating conditions:

charge = primary gasoline temperature = 775 ° C

H ₂ O / charge = 0.8 wt.

residence time = 0.1 s

Table IV provides a comparison of the results obtained with steam cracking of primary gasoline in a fixed bed apparatus in the presence of mayenite prepared as described in Example 1 and in the presence of vanadium oxide-enriched mayenite in the latter case. A sample enriched in vanadium pentoxide was prepared as described in the Example

Third

. The results show that vanadium added as an oxide also has a positive effect on the catalyst performance under cracking conditions and that it increases the overall yield of more valuable products such as ethylene and propylene.

r r

X-ray diffraction spectrum of pure mayenite phase c c r r r r r r '- c.

Table I

20 ° (CuKa) (°) d (xl0 ^'10 meters) 18.18. 4.88 21.02 4.22 23.52 3.78 27.89 3,196 29,87 2,989 33.48 2,675 35.17 2,550 36.77 2,442 38.33 2,347 41.31 2,184 44.10 2,052 46.76 1,941 49.30 1,847 51,76 1,765 52.96 1,728 54,14 1,693 55.30 1,660 56.44 1,629 57,56 1,600 60,87 1,521 61.94 1,497 62.98 1,475 67.19 1,392 69,23 1,356

Table II

X-ray diffraction spectrum of a sample formed by mayenite

Cai ₂ Al ₁₄ O ₃ 3 and Powellit CaMoO ₄

20 ° (CuKa) (°) d (x 10 ^-10 M) mayenite d (x 10 ^-10 M) powellite 18,18 4.88 18.68 4.75 21.02 4,22 ' 23.52 3.78 27.89 3,196 28,80 3,097 29,87 2,989 31.33 2,853 33.48 2,675 34.34 2,609 35.17 2,550 36.77 2,442 38.33 2,347 . 39.38 2,286 39.95 2,255 41.31 2,184 44.10 2,052, 46.76 1,941 47,11 1,927 49.30 1,847 51,76 1,765 52.96 1,728 54,14 1,693 55.30 1,660 56.44 1,629 57,56 1,600 58.05 1,588 59.59 1,550 60,87 1,521 61.95 1,497 62.98 1,475 67.19 1,392 69,23 1,356

r e

Table III

Yield (% w / w) 12CaO.7Al ₂ O ₃ 12CaO.7Al ₂ O ₃ + 2% MoO ₃ hydrogen 1.16 1.57 methane 12.65 11.43 ethylene 26.08 26.97 ethane 2.79 2.96 propylene 15,30 16.63 propane 0.40 0.42 butanes 1.80 1.73 Butenes + butadiene 5.57 6.31 CO + CO ₂ 0.17 0.51 Total gas 65.92 68.52 coke 0.11 0.50 Total ethylene + propylene 41,38 43,59

Table IV

Yield (% w / w) 12CaO.7Al ₂ O ₃ 12CaO.7Al ₂ O ₃ + 2% V ₂ O ₅ · hydrogen 0.94 1.50 methane 11.14 13,12 ethylene 26,27 27,15 ' ethane 2.52 3.50 propylene 17.60 17.87 propane 0.48 0.48 butanes 2.04 1.45 butene 7.35 6.48 butadiene 5.03 4.86 CO + CO ₂ 0.03 0.20 Total gas 73,4 76.6 coke 0.4 0.5 Total ethylene + propylene 43.87 45,02

? P and -200C

Claims (11)

PATENT REQUIREMENTS ς · ~ r f r z <. n r c '· rc' · '' e Γ Γ Γ. · R. · Cc r. rr - c c · ť · <r. r,. ··. r c - r i · A catalyst for steam cracking reactions comprising at least one crystalline calcium aluminate having a CaO / Al ₂ O ₃ molar ratio ranging from 1/6 to 3 and molybdenum and / or vanadium oxide, wherein molybdenum oxide expressed as MoO ₃ or oxide % vanadium, expressed as V ₂ O _5, or the sum of the two oxides ranges from 0.5 wt. % to 10 wt. Catalyst according to claim 1, characterized in that the molybdenum oxide expressed as MoO ₃ or the vanadium oxide expressed as V ₂ Os or the sum of the two oxides ranges from 0.8% by weight. % to 5 wt. Catalyst according to claim 1 or 2, characterized in that the crystalline calcium aluminate has a CaO / Al ₂ O 3 molar ratio corresponding to 12/7 or 3. Catalyst according to claim 3, characterized in that the crystalline calcium aluminate having a CaO / Al ₂ O ₃ molar ratio corresponding to 12/7 is pure mayenite. Process for preparing a catalyst according to any one of claims 1 to 4, characterized in that it comprises the following steps: dissolving the molybdenum or vanadium-containing salt in a suitable solvent; impregnating the calcium aluminate present in the form of granules by adding said aluminate to the molybdenum or vanadium salt solution; elimination of the solvent; drying the solid precursor product at temperature 100 ° C to 150 ° C; - annealing the solid precursor product at temperature 500 ° C to 650 ° C for at least 4 hours. A process according to claim 5, wherein the molybdenum salt is ammonium heptamolybdate tetrahydrate. The process according to claim 5, wherein the vanadium salt is vanadium acetylacetonate. Process according to claim 5 for preparing a catalyst according to claim 4, characterized in that the pure mayenite is obtained using the following steps: - dissolving calcium and aluminum containing salts in water; complexing the dissolved salts with polyfunctional organic hydroxy acids; drying the solution obtained in the preceding step to form a solid precursor product; - annealing the solid precursor product at temperature 1300 ° C to 1400 ° C, preferably 1330 ° C to 1370 ° C, for at least 2 hours. The process according to claim 8, characterized in that the calcium-containing salts are selected from calcium acetate and calcium nitrate, the aluminum-containing salt used is aluminum nitrate and the polyfunctional hydroxy acid is citric acid. The process according to claim 8, wherein the molar ratio of polyfunctional hydroxy acids / calcium-aluminum salts ranges from 1.5 to 1. 1.1. Process for producing light olefins by steam cracking reaction of hydrocarbon feedstocks selected from petroleum, kerosene, gaseous oil and mixtures thereof in the presence of a catalyst according to one of claims 1 to 4, characterized in that it is carried out at a temperature of 720 ° C to 800 ° C. 111 kPa to 182 kPa and for a contact time of 0.07 to 0.2 s. The method of claim 10, wherein the oil is a primary gasoline.